In eight hospitals from coast to coast, volunteers will receive a series of shots, some stronger than others to figure out how much vaccine, and how many shots, it will take to protect the public.

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Volunteers will get two shots, three weeks apart, while researchers look at the swine flu vaccine's safety, effectiveness, and whether it will take one dose or two to provide immunity.

"We'll collect a blood specimen at every visit to measure the antibodies to the vaccine," explained Dr. Lisa Jackson, the researcher leading the trials at Group Health Cooperative in Seattle.

Volunteers like Paul Ritterhoss will be closely monitored for the next several weeks. While doctors say the process is safe, Ritterhoss and others risk fever, allergic reactions and a remote chance of paralysis and even death.

"The opportunity to contribute to something that is really on the cutting edge of science, that has significance to lots of people around the world, is something that makes the risk worth it," Ritterhoss said.

Fellow vaccine volunteer Cynthia Thomsen said she was not worried, either.

"I trust what they are doing and I think it is great what they are doing. I think you need to do things like this to benefit others," Thomsen said.